1. Technical Field
This invention is concerned with a disc brake system, for example for a wheel of a vehicle.
2. Related Art
A conventional disc brake system comprises a hub mounted on a suspension link for rotation relative thereto, the hub providing a mounting for a wheel, and a disc brake comprising a brake disc mounted for rotation with the hub, friction material pads arranged on opposite sides of the disc, and at least one piston and cylinder assembly operable to urge the pads into engagement with the disc, to brake the hub and hence the wheel. Conventionally, the piston and cylinder assembly is slidably mounted on a slide bolted to the suspension link of the vehicle. The disc is conventionally rigidly fixed to the hub, and wear of the pads and/or the disc is accommodated by the sliding movement of the cylinder.
Disc brake systems are known in which the disc rotates with the hub as a unit but can perform sliding movement on the hub. For example, see GB 1 396 503. However, such systems are associated with technical problems. For example, since the discs are relatively thin, they tend to tilt on the hub and affect the braking ability. Also, there is a tendency for noise to be produced by rattle of the disc against the hub. At higher disc temperatures, these problems can be particularly severe since, when there is a large temperature differential, such as 600xc2x0 C., between the braking surface of the disc and the hub, the disc expands considerably, away from the hub, exacerbating the problems of tilting and rattle. These problems are addressed in WO 98/26192 in which the solution proposed is to provide a plurality of resilient force applicators which are mounted between the hub and the disc, the force applicators acting to apply radially-directed forces to the disc to control the movement thereof, the force applicators being distributed circumferentially around the hub. In one of the embodiments proposed in WO 98/26192, the force applicators are leaf springs and each leaf spring may be secured to the outer surface of the hub in a manner such that the spring extends tangentially of the hub when the disc is not mounted on the hub. The spring is resiliently deformed when the disc is mounted on the hub. The central portion of each leaf presses against the hub while the extreme ends thereof press against the disc. Thus, in the case of 3 leaf springs as shown in FIG. 1 of WO 98/26192, the disc is engaged at 6 points by the springs. DE 2039003 A discloses use of springs to apply radially-directed forces between a slidable disc and its hub, the springs being shaped leaf springs with their centres bearing on one of the hub or the disc and their ends bearing on the other.
It is an object of the present invention to improve the control of the movement of a disc on a hub provided by leaf springs similar to those disclosed in WO 98/26192.
The invention provides a disc brake system comprising a disc, and a hub which is arranged to rotate about an axis thereof, the system also comprising mounting means by which the disc is mounted on the hub so that the hub and the disc rotate as a unit about said axis and the disc can perform axial sliding movement on said hub, the system also comprising a plurality of leaf springs mounted on the hub and engaging the disc so that the springs apply radially-directed forces between the disc and the hub, characterised in that each of said springs comprises at least three abutments which project transversely of the spring and engage the disc so that the abutments apply forces to the disc.
In a disc brake system according to the invention, the abutments each provide a point of contact with the disc so that the number of points of contact between the disc and each spring is increased, in comparison with the system disclosed in WO 98/26192. This reduces the force acting at each such point of contact. This gives improved control of the disc movement.
A disc brake system according to the invention may be of the type disclosed in WO 98/25804. That brake system comprises two discs which are slidable on the same hub under the control of leaf springs which act between the hub and the discs. The system also comprises a cylinder which is integrally formed with a suspension link and a caliper also fixed to the suspension link, the caliper having supports for friction pads mounted thereon. In such a system, leaf springs as disclosed herein replace the leaf springs disclosed in WO 98/25804 which act between the hub and the discs.
In a disc brake system according to the invention, said abutments may be provided by embossed portions of the spring. Such embossments may have a generally semi-cylindrical form. Alternatively, the abutments may be provided by material deposited on the spring and secured thereto.
Said abutments may be elongated so that each abutment remains in engagement with the disc throughout said movement of the disc on the hub.
Said abutments may be in the form of ridges extending parallel to the axis about which the hub rotates.
The leaf springs of a disc brake system according to the invention may be secured to the outer surface of the hub in a manner such that the springs extend tangentially of the hub when the disc is not mounted on the hub.
In a disc brake system according to the invention, cut-outs may be formed in the leaf springs to control the force applied by the abutments to the disc. Such cut-outs may be in the form of holes through the spring or may be cut into the edges of the spring.
A disc brake system according to the invention may comprise one or more further discs mounted on the hub. In this case, each leaf spring may have abutments which engage all of the discs. Alternatively, the leaf springs may be arranged in groups, one spring in each group being associated with each disc, at least one spring in each group being retained in position by a connection to another spring in said group.
Said mounting means of the disc on the hub may comprise axially-extending grooves formed in an external surface of said hub and teeth projecting from said disc into said grooves, the teeth being a sliding fit in said grooves. In this case, said leaf springs may be located within said grooves and engage said teeth.